Self-nanoemulsifying drug delivery systems for oral insulin delivery: in vitro and in vivo evaluations of enteric coating and drug loading

This study aims at evaluating the combination of self-nanoemulsifying drug delivery systems (SNEDDS) and enteric-coated capsules as a potential delivery strategy for oral delivery of insulin. The SNEDDS preconcentrates, loaded with insulin–phospholipid complex at different levels (0, 2.5 and 10% w/w), were readily dispersed in water to form nanoemulsions of 35 nm and vesicles of 300 nm. The association efficiency of non-complexed insulin in the dispersed SNEDDS was 18.6%, and was increased to 73.1% for insulin–phospholipid complex (at 10% loading level). The morphology of the dispersed SNEDDS changed from nanoemulsion droplets to vesicular structures with increasing complex loading levels. A pHdependent insulin release profile was observed for SNEDDS filled into capsules coated with the enteric polymer, Eudragit1 L100. Using a Caco-2 cell model, it was observed that the transport of insulin was enhanced by factors of 7.7- and 9.3- for SNEDDS loaded with 2.5 and 10% complex, respectively. In healthy fasted rats, administration of SNEDDS (10% complex) filled in enteric-coated capsules produced a 2.7-fold and 3.4-fold enhancement in the relative bioavailability and glucose reduction, respectively. This study shows the effectiveness of combining SNEDDS (loaded with insulin–phospholipid complex) with entericcoated capsules for enhancing the oral absorption and efficacy of insulin. Refereed/Peer-reviewed